Presently known restraint systems for vehicles include driver and passenger side air bags which are housed in the steering wheel and in the dashboard, respectively, in a collapsed, folded condition and are adapted to be deployed instantaneously by introduction of a gas—sometimes referred to herein as “air”—upon the occurrence of a collision. Additionally, the automotive industry has introduced air bags which are housed in the rear supports of the front seats or in the rear seats to protect the cabin occupants in the event of a collision occurring on either side of the vehicle. Moreover, a further safety feature that has been made available for passenger vehicles, especially the so-called sport utility vehicles (SUVs), are air-holding side impact protective inflatable side curtains which are designed to provide a cushioning effect in the event of rollover accidents. These side curtains are housed uninflated in the roof of the vehicle or in one of the main support pillars of the vehicle, and deploy along the interior sidewalls of the cabin of the SUV in the event of a rollover.
In addition to the widely used flat textile fabrics that are coated and then sewn or stitched to form an air bag, there has more recently been introduced into this field one-piece woven fabrics (OPW) that are woven as preformed air bags or side curtains with preconfigured air-holding cavities that require little or no further sewing or stitching in the formation of the bag. These OPW fabrics, mainly used in the construction of side curtains, require only an exterior surface coating to retain air.
Each of these different types of air bags has different design and physical property requirements, such as air holding, air permeability, air pressure and volume, puncture resistance and adhesion of the coating material to a woven fabric. For example, driver side air bags must have little or no permeability and, as a result, are often made from a material having very little or no permeability. Passenger side air bags, on the other hand, require a controlled permeability, and are most often made from materials having some degree of permeability. Furthermore, all such vehicle air restraint devices must have superior packageability and anti-blocking qualities. Packageability refers to the ability for a relatively large device to be packaged (stored) in a relatively small space. Anti-blocking refers to the ability of the device to deploy almost instantaneously from the stored condition without any resistance caused by the material sticking to itself. This is an important consideration in an air bag or side curtain which could remain stored for long periods of time before it is activated.
The air holding capability of side curtains is critical since they must remain inflated for an extended period of time to protect passengers in multiple rollovers. Unlike air bags which are designed to inflate instantaneously, and to deflate almost immediately after inflation in order to avoid injury to the driver and front seat passenger, air curtains used in SUVs, or in ordinary passenger vehicles, must be capable of remaining inflated in the range of from about three (3) to about twelve (12) seconds, depending upon the size of the curtain and the type of vehicle. An average passenger vehicle would require a side curtain of from about 60 inches to about 120 inches in length as measured along the length of the vehicle, while a larger vehicle, such as a minivan, would require an even longer side curtain. The maximum inflation period of a side curtain should be sufficient to protect the cabin occupants during three (3) rollovers, the maximum usually experienced in such incidents.
When such air bags are deployed, depending upon their specific location or application, they may be subjected to pressures within a relatively broad range. For example, air bag deployment pressures are generally in the range of from about 50 kilopascals (kpa) to about 450 kpa, which corresponds generally to a range of from about 7.4 pounds per square inch (psi) to about 66.2 psi. Accordingly, there is a need for fabric products and air bags that can be made to be relatively impermeable to fluids under such anticipated pressures while being of relatively light weight.
One means of improving air holding capability in vehicle restraint systems has been through coatings, such as chloroprene and silicone rubber coatings, which are applied to the textile substrate. However, these coated air bags are not susceptible to heat sealing and are usually made by stitching, a process that requires the addition of an adhesive sealant in the stitched areas. To alleviate this problem there have been developed improved polyurethane, acrylic, polyamide and silicone coatings that are coated singly or in layers on the fabric substrates. It has been disclosed in the art, for example, in Menzel et at., U.S. Pat. No. 5,110,666, to coat a woven nylon substrate with polyurethane to provide the desired permeability to better retain the inflation gas. Certain aqueous silicone emulsion coating compositions that yield a tack-free surface and high mechanical strength to prevent cracking on inflation of the air bag have also been disclosed in the art, such as, for example, in Inoue et al., U.S. Pat. No. 5,254,621.
Wherever coated fabrics are used, however, there exists the problem of insufficiency of adhesion of the coating to the fabric substrate. More particularly, the smoother the substrate surface, generally the more difficult it is to obtain strong adhesion of the coating material to the substrate. Therefore, much attention has been paid to the problems associated with adhesion of coatings to woven substrates, and in particular to multiple coatings of one or more polymeric materials on woven and non-woven fabric substrates of polyesters and polyamides, including combinations as well as mixed deniers of those fabric substrates. Examples of such coated fabric substrates, coating materials and methods of coating such fabrics are disclosed in commonly assigned U.S. Pat. Nos. 6,239,046; 6,350,709; 6,455,449; 6,458,724; 6,641,686; 6,645,565; and 6,734,123, the disclosures of each of which are incorporated by reference herein and made a part of this disclosure.
Despite advances in air bag coating technology, there remain problems related to the controlling of air permeability, air pressure, and volume. In particular means to accomplish these important functions while at the same time reducing the already high cost of production of air bags and side curtains in a highly cost competitive environment is of paramount concern. In this respect, polysiloxane coatings are very expensive and OPW fabrics often require a second coating of polyurethane to accomplish the sealing effect required for a side curtain. Polyvinyl chloride coatings are much less expensive than polysiloxane coatings, but have not been considered acceptable for use as air bag coatings because of problems of adhesion (sticking) due to the relatively low melting point of polyvinyl chloride compared to polyurethane and polysiloxane. Moreover, it was thought that polyvinyl chloride would not work well in air bags as a result of adhesion or sticking during long periods of storage because of its relatively low melting point. The problem of sticking became of increasing concern with the advent of the OPW air bag fabric used in side curtains, which have two interior facing inflation surfaces that must not stick together when the air bag is deployed.
I have invented a product and process by which polyvinyl chloride is used to coat flat woven air bag fabric as well as prefabricated OPW fabric for use in side curtains. The polyvinyl chloride-coated products of this invention are typically used, preferably in conjunction with so-called cold inflators, and can be used alone or in combination with polyurethane coatings, if desired. The polyvinyl chloride coatings of the invention provide substantially equally effective air holding capability and aging characteristics as do the polysiloxane and polyurethane coatings of the prior art and adhere well to polyester woven fabrics commonly used in air bags and side curtains. Moreover, when the polyvinyl chloride coatings are used in combination with polyurethane coatings, additional benefits in terms of air holding capability are obtained.